The present invention relates to measurement standards and more particularly to a standard for checking the accuracy of a coordinate measuring machine (CMM).
A coordinate measuring machine (CMM) measures objects by making contact in a variety of locations, and recording the x, y and z location of the probe, as described in U.S. Pat. Nos. 4,168,576 and 4,364,182, which are hereby incorporated herein by reference. After all the contact points are collected, the coordinates are mathematically compared to an ideal geometric shape. The CMM displays the characteristics of the object to the user. The kinds of characteristics that might be displayed include the object's size, its relative position to an established coordinate system, and often, its deviation from an ideal geometric shape.
The geometric shapes which can be measured or detected by a CMM are: sphere, circle, flat surface (e.g., a plane), cone, cylinder, ellipse, line, and point.
However, the CMM itself must be calibrated. Current practice in contact type CMM calibration uses a qualified sphere to establish the calibration of the contact probes. Noncontact CMMs, such as those using reflected laser beams or other methods of determining the distance from the CMM's probe to the object, may use a variety of calibration masters for initial machine calibration.